Techniques for polynucleotide detection have found widespread use in basic research, diagnostics, and forensics. Polynucleotide detection can be accomplished by a number of methods. Most methods rely on the use of the polymerase chain reaction (PCR) to amplify the amount of target DNA.
The TaqMan™ assay is a homogenous assay for detecting polynucleotides (U.S. Pat. No. 5,723,591). In this assay, two PCR primers flank a central probe oligonucleotide. The probe oligonucleotide contains two fluorescent moieties. During the polymerization step of the PCR process, the polymerase cleaves the probe oligonucleotide. The cleavage causes the two fluorescent moieties to become physically separated, which causes a change in the wavelength of the fluorescent emission. As more PCR product is created, the intensity of the novel wavelength increases.
Molecular beacons are an alternative to TaqMan (U.S. Pat. Nos. 6,277,607; 6,150,097; 6,037,130) for the detection of polynucleotides. Molecular beacons are oligonucleotide hairpins which undergo a conformational change upon binding to a perfectly matched template. The conformational change of the oligonucleotide increases the physical distance between a fluorophore moiety and a quencher moiety present on the oligonucleotide. This increase in physical distance causes the effect of the quencher to be diminished, thus increasing the signal derived from the fluorophore.
U.S. Pat. No. 6,174,670B1 discloses methods of monitoring hybridization during a polymerase chain reaction which are achieved with rapid thermal cycling and use of double stranded DNA dyes or specific hybridization probes in the presence of a fluorescence resonance energy transfer pair—fluorescein and Cy5.3 or Cy5.5. The method amplifies the target sequence by polymerase chain reaction in the presence of two nucleic acid probes that hybridize to adjacent regions of the target sequence, one of the probes being labeled with an acceptor fluorophore and the other probe labeled with a donor fluorophore of a fluorescence energy transfer pair such that upon hybridization of the two probes with the target sequence, the donor fluorophore interacts with the acceptor fluorophore to generate a detectable signal. The sample is then excited with light at a wavelength absorbed by the donor fluorophore and the fluorescent emission from the fluorescence energy transfer pair is detected for the determination of that target amount.
There are also several other fluorescent and enzymatic probes for polynucleotide detection, such as Scorpions™, Sunrise™ primers, and DNAzymes, where each polynucleotide to be detected requires a different oligonucleotide probe and two different fluorescent moieties. These probes are usually custom-synthesized and are thus expensive.